This invention relates to ultrasonic transducers in general and more particularly to an improved method of manufacturing ultrasonic transducers.
Copending patent application U.S. application Ser. No. 265,449 discloses a method for manufacturing an ultrasonic transducer arrangement with transducer elements which are provided with contact tabs made of a contact foil. According to this method, at least one flat side of a plastic foil serving as the contact foil is provided with a metal deposit which is undetachably connected to a flat side of a strip-shaped piezoelectric body. The other flat side of the contact foil is fastened to a damping body, whereupon a subdivision of the piezoelectric body is carried out. According to a further embodiment of the method, a divided contact foil can be used, the metal coating of which is then connected to a respective edge zone of the piezoelectric body only in the edge region. The piezoelectric body is likewise provided with metallization on its flat sides. In the ultrasonic transducer arrangement to be manufactured, several respective adjacent transducer elements are to form a transducer group of transducer elements which are acoustically separated and are electrically controlled in common.
The contact foil always forms a common feed for the electric transducer elements of a transducer group having elements which are electrically connected in parallel. For acoustical reasons, a very thin contact foil is chosen, the thickness of which generally does not exceed 10 .mu.m appreciably and is preferably considerably less than 10 .mu.m. The thickness of the metal coating is still substantially smaller than the thickness of the contact foil. It must always be connected undetachably to a narrow side of the transducer elements, the width of which, in an ultrasonic transducer array with several hundred transducer elements for high frequencies of, for instance, 5 MHz and more, can, in some circumstances, be considerably less than 100 .mu.m. The contact foil must therefore be connected to a correspondingly narrow surface part of the transducer elements. If sufficient contact is not brought about over this small surface area during the soldering operation or if the solder connection opens up again during the subsequent, generally mechanical subdivision of the piezoelectric body, the current supply to this transducer element is interrupted and this element therefore will not be active during the operation of the ultrasonic transducer arrangement. In the subsequent subdivision of the piezoelectric body for making the individual transducer elements, the cuts are taken perpendicularly to the flat sides of the piezoelectric body to such a depth that even the electrically conducting surface layer of the contact foil is mechanically separated between the individual transducer elements. The parts of the contact foil which remain at the ends of the transducer element and serve as the current lead for one of the transducer elements are therefore no wider than the tranducer elements produced and their mechanical strength is accordingly low. In connecting the contact tab, to be made later, to an electric control lead, which is in general located on a control plate, the connection to one of the transducer elements can be interrupted by mechanical damage. The electric lead can furthermore be disturbed by a crack formation in the metal coating in the vicinity of the end faces of the transducer elements.